The present invention relates to a memory device and a storing method and relates to, for example, a memory device and a storing method that store data that is required to be stored for a finite period of time.
When security information such as key information or authentication information is stored in a memory device, time during which the memory device holds the security information may be preferably finite for security or operational reasons. It is therefore required to provide a memory device capable of erasing stored information after an elapse of a finite period of time.
Japanese Unexamined Patent Application Publication No. 2007-109148 or Japanese Unexamined Patent Application Publication No. 2006-059228 is one example of the above technique. Japanese Unexamined Patent Application Publication No. 2007-109148 discloses an external memory device that stops a refresh operation of a DRAM and erases stored data when time of a timer has reached a predetermined time. Japanese Unexamined Patent Application Publication No. 2006-059228 further discloses a memory device that interrupts power supply to a volatile memory when a specific phenomenon has occurred.